1. Field of the Invention
This invention relates to a position sensor and, more specifically, to a microwave position sensor using a solid state transistor or diode oscillator and antenna coupling.
2. Brief Description of the Prior Art
In general, there are presently three types of position sensors available. The most commonly used type, for example, in anti-skid brake systems includes a pickup coil which transmits a current pulse when a magnet passes across the coil. This design is rugged and low cost, however it has a useful output only when the wheel turns at a predetermined minimum angular velocity. The second type of position sensor, which uses the magnetoresistance principle, can detect zero angular velocity, however the output critically depends upon the spacing between a sensor and a magnet. Normally, such a constant space on the order of 100 mils can not be maintained easily in a rotating wheel. The third type of position sensor, which uses the Hall effect, has the advantage that a preamplifier can be designed and merged with the Hall sensor. Thus, the output can be made considerably larger than the magnetoresistance sensor. However, the Hall sensor also suffers from spacing requirement. Furthermore, it is more sensitive to temperature, thereby making it less valuable for use in conjunction with automobile electronics. It is therefore apparent that a position sensor which can overcome the above noted deficiencies of the prior art is sought and would be useful, particularly in the anti-lock braking systems (ABS) which are presently replacing the prior art automotive braking systems.